Precise droplet injection for calibrating a gas chromatography instrument

ABSTRACT

A method and apparatus for calibrating a gas chromatography instrument by forcefully shooting a measured droplet which securely passes through a confined passageway without direct intervention of human hands into the entry throat of the instrument so as to avoid contaminating the apparatus or impairing the accuracy of the instrument.

This is a divisional application which claims priority of our priorcopending application Ser. No. 11/821,593 filed Jun. 22, 2007, now U.S.Pat. No. ______, and also claims priority or our Provisional ApplicationSer. No. 60/850,197 filed Oct. 5, 2006.

FIELD OF INVENTION

Gas Chromatography instruments and the procedure for calibrating them.

PRIOR ART

Prior art patents include:

-   -   Staples and Watson Pat. No. 5,289,715, issued 1994.    -   Staples Pat. No. 6,212,938 issued 2001.    -   Johnson et al Pat. No. 6,983,636 issued 2006.

BACKGROUND OF THE INVENTION

Controlling and measuring very small quantities of fluid is required inmany environments and for many purposes. For example, medical testingprocedures as shown in the Johnson et al Pat. No. 6,983,636 issued in2006 may require the repetitious application of droplets of identicalsize. Ink-jet printers require precise control of the flow of very smalldroplets of ink into their various output openings, and may utilizetechniques such as those shown in the Starr Pat. No. 4,818,706 issued in1989 or the Shimano Pat. No. 5,277,333 issued in 1994. In the Meinhartet al Pat. No. 7,057,198 issued in 2006 a technique is shown formeasuring extremely small velocities of a flowing fluid.

The calibration of a gas chromatograph instrument, however, poses asomewhat different problem. Gas chromatography instruments identify thenature and smell of a gas by measuring the quantities of its differentconstituents. From time to time such an instrument may requirecalibration or re-calibration, due to various factors that have changedeither within the instrument itself or in its environment. It has been acommon calibration practice to inject a droplet of a known compound intothe inlet or throat of the chromatograph instrument and compare theresponse of the instrument with a known standard. The Kovat Index of theinjected droplet may be utilized in completing the comparison.

The calibration of a gas chromatography machine has often beenaccomplished by manual use of a syringe to inject the test droplet intothe inlet or throat of the chromatography instrument. When a syringe isused there are disadvantages. Syringes are fragile and are dangerous touse because of the sharp needle. Syringes are also easy to contaminateand require special handling techniques. It is also difficult for anoperator to control the syringe for accurately aiming the droplet intothe inlet or throat of the machine. Mis-direction of the droplet maycause contamination of the precision chromatography instrument and thusadversely affect the accuracy of its subsequent measurements.

SUMMARY OF THE INVENTION

The purpose of the present invention is to allow the preciseintroduction of a diluted sample compound into an instrument whichmeasures that compound for the purpose of calibration of the instrument.According to the invention a sample droplet of a known compound isforcefully shot into the inlet or throat of the instrument. Only thesample contacts the instrument inlet, and the injecting apparatus ordevice does not. Thus the present invention eliminates use of the hardto master injection by syringe, and prevents subsequent contamination ofthe precision instrument.

According to the presently preferred apparatus of the invention a singlesample droplet with a precisely measured volume is supplied through apulse valve to a precise target. The test apparatus is aligned in placeboth axially and angularly to assure that the droplet moves along anaccurate coaxial trajectory into the throat of the precision instrument.A flexible boot is used to correctly interface between the dropletgenerator and the chromatograph, so that any wavering of the operator'shand will not adversely affect the trajectory of the droplet to beinjected. Droplet generator action is initiated by a manual control andis otherwise automatic.

The droplet is created by pressurizing liquid contained in a vial. Thepressurized liquid from the vial is directed to a pulse valve byappropriate tubing compatible with the sample. The duration of the pulseis selected by a selection means contained on an electronics board. Apush button switch activates generation and injection of the sample.When power is applied, a precise electrical signal is imposed on thepulse valve opening it for a selected time on the order of microsecondsto milliseconds.

The droplet is aimed at the inlet of a precision instrument through theflexible boot in such a way as to shoot it along a trajectory that isessentially coaxial with the throat of the instrument.

Further according to the invention the calibration may be performed on agas chromatography machine of the type that displays a closed-figurepolar diagram representing constituents of a sample received in thethroat of the machine. There will then be displayed on the screen of themachine an accurate vapor image which will enable the operator toestablish by pattern recognition that the calibration of the instrumentis correct.

DRAWING SUMMARY

FIG. 1 is an artistic schematic drawing illustrating the method ofoperation of the present invention;

FIG. 2 is an electro-mechanical block and line diagram of the presentlypreferred form of the apparatus according to the invention;

FIG. 3 is a perspective view of the interfitting parts of the testapparatus of the present invention and a gas chromatography machine withwhich it may be used; and

FIG. 4 is a cross-sectional view showing how the interfitting partsachieve alignment of a droplet to be ejected into the throat of thechromatograph.

INCORPORATION BY REFERENCE

Applicants hereby incorporate by reference the entire drawings,description, and claims of U.S. Pat. No. 6,212,938 issued in 2001, thesame as if it were fully set forth herein. The type of machine disclosedin U.S. Pat. No. 6,212,938 is currently sold under the trademark ZNOSE.That type of gas chromatography machine displays on an electronic screena closed-figure polar diagram representing the constituents of a vaporsample received in the throat of the machine, enabling an operator topromptly identify the vapor by pattern recognition.

Outline of the Method of Present Invention FIG. 1

Reference is now made to FIG. 1 wherein the method of the presentinvention is schematically shown. Test apparatus 20 includes a dropletgenerator 22 and a flexible boot 15. Droplet 14 is ejected from thegenerator and is shot outward through the boot 15 on a trajectory asindicated by a dotted line 24 that is essentially coaxial to the inletthroat 28 of a gas chromatograph 26. To aid in the proper alignment ofthe droplet generator to the inlet or throat of the test instrument theflexible boot 15 may be designed either to fit around the throat 28 ofthe chromatograph as illustrated, or else to fit inside it. Thechromatograph is illustrated as being of the type shown in the issuedPat. No. 6,212,938; that is, the instrument 26 is capable of generatingon an electronic display screen a closed-figure polar diagram 30 that isunique to the substance that was input to the machine. This then enablesan operator to identify by pattern recognition the particular vaporreceived at the input of the machine. In the present illustration thescreen display uniquely represents marijuana, but tests would more oftenbe made with a compound of known chemical characteristics, other thanmarijuana.

Part Names and Numbers

-   1. Vial or tank or reservoir-   2. liquid sample in the vial 1-   3. stopper for the vial-   4. cap for the vial-   5. tubing through stopper 3 to supply pressure in vial-   6. pump generating pressure for tubing 5-   7. tubing out from stopper to carry droplet 14-   8. pulse valve receiving droplet from tubing 7-   9. check valve in tubing 5 to prevent backflow-   10. electronic control board-   11. battery for electronic circuit-   12. start switch-   13. timing selector for pulse width-   14. ejected droplet-   15. flexible boot-   20. test apparatus and its housing-   22. droplet generator-   24. trajectory of droplet 14-   26. gas chromatography instrument-   28. inlet or throat of instrument 26-   30. closed polar-diagram display on 26-   32. outlet tube from pulse valve-   34. rigid housing to align pulse valve-   48. pulse valve rigid outer wall-   50. flat face of chromatograph 26-   52. cylindrical opening in 50-   54. circumferential rim on end of 34

DETAILED DESCRIPTION OF THE APPARATUS FIGS. 2-4

Reference is now made to FIG. 2 which illustrates the electro-mechanicalapparatus of the invention in a block and line form. The purpose of thepresent invention is for precise introduction of a diluted samplecompound into an instrument 26 which measures that compound for thepurpose of calibration of the instrument. According to the invention asample droplet 14 of a known compound is forcefully shot into the inletor throat 28 of the instrument 26. Only the sample droplet 14 contactsthe instrument inlet, and the injecting apparatus or device does not.Thus the present invention eliminates use of the hard to masterinjection by syringe, and prevents subsequent contamination of theprecision instrument. A vial or tank or reservoir 1 holds the liquid 2from which a sample is to be taken. The otherwise open bottom end of thevial or tank 1 is closed by a stopper 3

Depending upon the type of chemical compound that is being used for thecalibration sample, the pump 6 may fill the tank with air pressure, asthe present drawing suggests, or else alternatively an inert type of gasmay be used for that purpose. The apparatus is mainly intended forsingle-shot operation, so the pump 6 will need to restore tank pressurefrom time to time.

An electronics board 10 is energized from a battery 11. An adjustablepulse width selector 13 provided on the electronics board offers anoption as to the length of time for which the pulse valve 8 will be on;that is, for the interval of time during which the sample material willbe flowing out from tank 1 to create the droplet 14. In the presentapparatus the on time for the pulse valve may be adjusted from a fewmicroseconds to a number of milliseconds, as desired.

The droplet 14 is created by pressurizing liquid contained in the vial1. The pressurized liquid from the vial is directed to a pulse valve 8by appropriate tubing 7 which is chemically compatible with the sample.The duration of the pulse is selected by the selection means 13contained on the electronics board 10. A push button start switch 12activates generation and injection of the sample by initiating power tothe pulse valve 8. When power is applied, a precise electrical signal isimposed on the pulse valve allowing it to open for a time on the orderof microseconds to milliseconds. The droplet 14 is aimed at the inlet orthroat 28 of a precision instrument 26 through a flexible boot 15 suchas to shoot the droplet along a trajectory 24 that is coaxial with thethroat 28 of the instrument.

The droplet 14 is created by pressurizing the vial or tank 1 via a smallpump 6 through a check valve 9 to prevent any back flow of pressure fromthe vial. The pump 6 is turned on for a brief interval (by circuitry notspecifically shown) each time the power is applied to the electronics,thus assuring that the pressure in the vial is will remain at itsmaximum in order to insure a repeatable droplet size for the nexttesting step. In the preferred embodiment the entire apparatus of boththe droplet generator 22 and the flexible boot 15 are very small and areincorporated into a single apparatus that may be conveniently held inone hand.

Test apparatus 20 has a rigid housing about the size of a conventionalmatch box, which may be conveniently held by hand, and within which thedroplet generating apparatus 22 is contained. The flexible boot 15,illustrated in schematic form in FIG. 1 and more specifically in FIG. 3,is a longitudinal section of a cylindrical foam or tubing. A rigidhousing 34 for the pulse valve 8 cooperates with the flexible boot andthe gas chromatography instrument 26 for aligning the droplet that is tobe injected with the chromatography instrument. More specifically, asshown in FIGS. 3 and 4, the pulse valve 8 also has an elongated rigidouter wall from which an elongated rigid outlet tube 32 projects. Asshown in FIG. 4, instrument 26 has an elongated inlet or throat 28. Asalso shown in FIG. 4, when the rigid housing 34 for the pulse valve 8abuts the face of the instrument 26 the droplet outlet tube 32 is thencoaxially aligned with the throat of the instrument. This ensures thatthe ejected drop will not spill onto the sides of the inlet 28.

More specifically, the pulse valve 8 with its elongated outlet tube 32is a commercially available product. Valve housing 34, a rigid memberpreferably made of TEFLON for its resistance to corrosive chemicals, isspecially designed to provide an interface between the dropletgenerating apparatus 22 and the instrument 26. Instrument 26 has a flatface 50 within which a cylindrical opening 52 allows axially alignedaccess to the inlet or throat 28 of the instrument. When pulse valve 8having its own rigid outer wall 48 is inserted into the removablehousing 34 the two devices are then in coaxial relationship to eachother and also to the outlet tube 32. Flexible boot 15 is placed withits forward end portion at the rearward end of pulse valve 8 and aboutthe rearward end portion of rigid pulse valve housing 34. The rearwardend portion of boot 15 is placed in engagement with the forward end ofthe housing of test apparatus 20. The operator may try to coaxiallyalign the droplet ejection tube 32 with the inlet or throat 28 of theinstrument, but will need the assistance of the mechanism to accomplishthat. As the test apparatus 20 is moved closer toward instrument 26 acircumferential rim 54 on the forward end of valve housing 34 will enterthe cylindrical opening 52 in the face of instrument 26, thus ensuringthe desired alignment relationship, even if apparatus housing 20 isinadvertently somewhat twisted or yawed relative to the inlet of thechromatograph. Thus, at the extreme of forward movement of the housing34, start switch 12 may be depressed to actuate the pulse valve, sendinga test droplet forcefully and in correctly aligned relationship into thethroat 28 of the gas chromatograph.

Further according to the preferred form of the invention the calibrationprocedure may be performed on a gas chromatography machine that displaysa closed-figure polar diagram representing the constituents of a samplereceived in the throat of the machine. This is the type of machinedisclosed in U.S. Pat. No. 6,212,938, which is sold under the trademarkZNOSE. There will then be displayed on the screen of the machine anaccurate vapor image which will enable the operator to establish bypattern recognition that the calibration of the instrument is correct.In the present illustration the diagram on the screen of the machineuniquely represents marijuana, but tests would more often be made with acompound of known chemical characteristics, other than marijuana.

It is important that according to the invention a single sample dropletwith a precisely measured volume is supplied to a precise target. Thetest apparatus is aligned in place both axially and angularly, utilizingthe alignment of apparatus that is achieved by the rigid housing 34 andthe flexibility of the flexible boot 15, to assure that the droplet 14moves along an accurate trajectory essentially coaxial with the throatof the precision instrument 26. The flexible boot 15 is used to moreconvenient provide a reliably correct interface between the dropletgenerator 22 and the chromatograph 26, so that any wavering of theoperator's hand will not adversely affect the trajectory of the dropletto be injected. The droplet generator action is initiated by manualstart switch 12 and is otherwise automatic, the metering of the droplet14 and its forceful propulsion through the air into machie throat 28occurring in an essentially simultaneous manner.

The sample droplet is preferably chosen from a primary list of thirteencompounds, normal alkanes, from C6H14 to C14H16 plus C16H18, C16H22,C20H20, and C22H24. These are hexane, heptane, octane, noneane, decane,tlridecane, tetradecane, hexadecane, octadecane, eicosane, and docosane.They are used to index the unknown peaks that the instrument wouldsubsequently measure, using Kovat's Index. Other mixtures will begenerated as required. The mixtures would be limited to solventscompatible with TEFLON, stainless steel, and KALREZ, for theirresistance to corrosive chemicals.

A size selection to determine the droplet size and the amount ofmaterial to be injected is dialed into the electronics board of theapparatus. The drop size is therefore very repeatable. The dropletvolume is less than 1/1000 of the container volume, so generatingseveral drops after the pump has last been turned on will notsignificantly affect the pressure, and therefore provides a veryrepeatable drop size. A timing adjustment associated with push buttonswitch allows the precision instrument to be used for multipointcalibrations, and is also adjustable for different sensitivities of theinstrument to different compounds.

In the presently preferred embodiment of the invention the flexible bootassembly includes a spring mechanism to align the injection with theinstrument so that the trajectory of the injected droplet is notdependent on the angle of the hand-held droplet injector mechanism.There is a coaxial interface ring that registers the injector to theinstrument coaxiallyk. This assures that the drop is injected dirdectlykinto the inlet of the instrument. If the operator had to hold theinjector against the inle of the instrument gy hand, even the slightestaxial yaw would allow the drop to strike a side wall of the inlet beforeit was fully ingested. This would diminish or destroy the accuracy ofmeasurement. But by pushing against the spring boot, the operator cancause the coaxial interface to remain facially interfaced as well,indendent of any tendency of the operator's hand to yaw or aimincorrectly.

Although the presently preferred form of our invention has beendisclosed herein in detail in order to comply with the patent laws, itwill nevertheless be understood that other modifications should beapparent to those skilled in the art, and that the scope of ourinvention is to be judged only by the appended claims.

TEFLON and KALREZ are trademarks of DuPont Corporation.

1. In the art of calibrating a gas chromatography instrument that has aninlet throat for receiving a gas whose characteristics are to beanalyzed, the method of: generating a droplet of a known substance andwhich has known chemical constituents; shooting the droplet through anaccurate trajectory that is essentially coaxial to the inlet throat ofthe instrument so as to assure that neither the droplet nor theinstrument will become contaminated in that process; and then comparinga reading from the instrument with the known constituents of thedroplet.
 2. The method of claim 1 in which the droplet is forcefullyshot through a pulse valve.
 3. The method of claim 1 in which thedroplet is generated by a droplet generator, and a flexible boot isutilized to align the droplet generator with the inlet throat of theinstrument.
 4. The method of claim 1 in which the gas chromatographyinstrument is of the type that displays a closed-figure polar diagramrepresenting the constituents of a vapor received in the throat of themachine, thus enabling an operator to establish by pattern recognitionthat the calibration of the instrument is correct.
 5. The method ofclaim 4 wherein the droplet is generated by a droplet generator, aflexible boot is utilized to align the droplet generator with the inletthroat of the instrument, and the droplet is forcefully shot from apulse valve in the droplet generator into the throat of the instrument.6. The method of claim 5 utilizing an apparatus wherein both the dropletgenerator and the flexible boot are very small and are incorporated intoa single apparatus that may be conveniently held in one hand.
 7. Aninstrument system for precisely analyzing and measuring the chemicalconstituents of a vapor, comprising: a gas chromatography machine havinga housing and an entry throat projecting outward from the housing forreceiving a sample of vapor to be analyzed, the machine also having anelectronic screen and being adapted to display on the electronic screena closed-figure polar diagram representing the constituents of a vaporsample received in the throat of the machine; an electronicallycontrolled metering and injection apparatus for producing a droplet of adesired liquid to be injected into the entry throat for the purpose ofcalibrating the machine; a flexible boot cooperatively attached to themetering and injection apparatus and selectively attachable to the inletthroat of the gas chromatography machine for providing a confinedpassageway within which the droplet may securely pass withoutcontamination or error; and the metering and injection apparatus beingadapted to shoot the droplet through the flexible boot into the inletthroat without intervention of human hands, whereby an accurate vaporimage on the screen enables the operator by pattern recognition todetermine that the calibration of the instrument was correct.
 8. A gaschromatography instrument and a test apparatus for calibrating it,comprising, in combination: the gas chromatography instrument having aflat face within which a cylindrical central opening is formed, and anelongated inlet throat extending from that opening in coaxial relationthereto; the test apparatus being contained in a hand held housing,having an electronically controlled droplet generator contained withinthe housing and a pulse valve that extends from the housing, the pulsevalve having a rigid cylindrical outer wall; the pulse valve also havinga droplet outlet tube which extends forward from one end thereof inconcentric relation to its rigid outer wall, and a pair of wiresextending from the other end of the pulse valve for connection to andactivation from the droplet generator; and a rigid housing fortemporarily aligning the pulse valve with the throat of the gaschromatograph when a test droplet is to be injected into the throat ofthe instrument, the rigid housing having an internal space for slidablyreceiving the pulse valve in a predetermined position relative thereto;the rigid housing also having a forwardly projecting circumferential rimportion that interfits in a predetermined relation with the cylindricalcentral opening in the face of the instrument with the droplet tubeprojecting forward.
 9. The apparatus of claim 8 which further includes asoft cylindrical flexible boot for supporting the rigid pulse valvehousing in adjustable relation to the housing of the hand held testapparatus when alignment with the gas chromatograph is being establishedfor purpose of injecting a test droplet.